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Pre-treatment of tantalum and niobium ores from Democratic Republic of Congo (DRC) to remove uranium and thorium

Kabende, Elie (2020) Pre-treatment of tantalum and niobium ores from Democratic Republic of Congo (DRC) to remove uranium and thorium. Masters by Research thesis, Murdoch University.

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Tantalum (Ta) and niobium (Nb) have applications in high-technology electronic devices and steel manufacturing, respectively. Africa, South America and Australia collectively provide about 80% of the global supply of Ta-Nb concentrates. In Africa, Sociéte Minière de Bisunzu (SMB) located in the Democratic Republic of Congo (DRC) remains the major supplier of Ta-Nb concentrates containing about 33 wt % Ta2O5 and 5 wt % Nb2O5 as the two oxides of main economic values, associated with uranium (0.14 wt %) and thorium (0.02 wt %). The presence of U and Th complicates the transportation logistics of tantalite to international markets, due to stringent regulation on an allowable limit of U and Th at 0.1 wt %. High radiation levels also hinder further primary beneficiation of the Ta-Nb concentrates at the Bisunzu mine to an extent of at least 50 wt % Ta2O5 and Nb2O5 combined. Digestion of the concentrate using HF is the conventional method to remove U and Th followed by chemical treatment to recover Ta2O5 and Nb2O5. The HF digestion process is hazardous and requires large investments. The main objective of this study is the mineral identification in the ore and concentrates of SMB mine sites, to investigate the possibilities of upgrading the Ta2O5 and the Nb2O5 by weight using physical separation and concentration, and removing U and Th using chemical treatment.

The mineral identification analysis conducted on eight concentrates sourced from different mining locations at the Bisunzu mine in DRC has shown that manganocolumbite, manganotantalite and ferrotantalite are the major phases with cassiterite, as well as pyrochlore and microlite group of minerals hosting uranium as minor components. The rare earth minerals, quartz and lepidolite were also identified in the ore and concentrates. The quantitative analysis revealed a chemical composition range of 20 – 47 wt % Ta2O5 and 5.4 – 22 wt % Nb2O5 as the principal oxides, associated with 0.005 – 0.802 wt % U and 0.001 – 0.072 wt % Th as radioactive elements. Due to high content of iron in concentrate, the magnetic separation of selected sample has shown an increase of Ta2O5 and Nb2O5 to 50 wt % and 19 wt %, respectively, in the non-magnetic portion. Samples with low content of iron have shown weak magnetic properties. Sieving of selected concentrates also increased 18 wt % Ta2O5 and 9 wt % Nb2O5 in coarse size fraction of –2800+1000 μm by about 100%. It was also observed that U and Th were more concentrated in the fines (–1000 μm) i.e., 4844 g/t U and 135 g/t Th compared to 1132 g/t U and 50.5 g/t Th in coarse particles.

The sulfuric acid bake of fine particles (–75 μm) at 300 oC for 2 h followed by leaching with H2SO4 and K2S2O8 at 90 oC for 3 h lowered the concentration of U and Th in the feed from 0.8 wt % and 0.03 wt %, respectively, to ≤ 0.01 wt %. The measured concentrations of dissolved metal ions (U, Th, Ta and Nb) show reasonable agreement with published solubility diagrams. An average of 7% Ta and 9% Nb dissolved in the bake-leach process with leaching efficiencies of 100% U and 60% Th. The reliability of the analytical methods and bake-leach results have been confirmed by the elemental mass balance calculation. The H2SO4 and CaF2 leaching at 90 oC dissolved 100% U and 90% Th along with 81% Ta and 43% Nb which warrants further investigations.

Item Type: Thesis (Masters by Research)
Murdoch Affiliation: Chemistry and Physics
Supervisor(s): Senanayake, Gamini, Deditius, Artur, Dugogorski, Bogdan, Oskierski, Hans and Altarawneh, Mohammednoor
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